Field of the Invention
This invention relates, in general, to sewing machines and, in particular, to a new and useful sewing machine having a lifting and feeding mechanism which includes an arrangement for insuring that the relative velocity of the top feed foot reduces substantially during its movement toward its touch-down on the material which is being sewn.
In a prior art top feeding device of this class (U.S. Pat. No. 3,570,427), a transmitting rocker arm for the lifting drive of the top feed foot is mounted on a support element of the support system in order for the top feed foot to be carried along in the upward direction during the lifting of the support system.
In this device, the lifting drive has an essentially sinusoidal movement pattern. As a result of this, the top feed foot reaches its maximum velocity upon touching down on the fabric to be sewn, so that vibrations may occur at high sewing machine speeds.
The present invention provides a movement pattern of the top feed foot in the top feeding device, so that the relative velocity of the top feed foot will reduce substantially during the touch down phase.
This task is achieved in an top feeding device for sewing machines which includes a sewing machine main drive shaft connected to a connecting rod mechanism for moving a transmitting rocker arm to achieve a lowering and lifting movement of a top feed foot and a material presser foot on a support of the sewing machine wherein a spring is provided biasing the presser foot downwardly. The movement is provided such that the feed foot touches down on the material to be sewn and feeds the material to a reciprocating swinging needle in order to have both the feed drive and the lifting drive moving the top feed foot so that its velocity decreases during is touch-down on the material. A drive mechanism is provided between the transmitting rocker arm and the presser foot. The rocker arm is provided with a common pivot. The drive mechanism includes a pair of first and second connecting rods mounted on the support and connected to the common pivot of the rocker arm.
The vertical component of movement acting on the top feed foot during its touch-down phase is reduced substantially by the device according to the present invention compared with the normally sinusoidal movement pattern, while the vertical movement component is increased outside the touch-down phase. The duration of the touch-down phase of the top feed foot is thus increased and the forces to be absorbed by the compression springs are reduced.
Even though devices for retarding the touch-down and lift-off movements of the top feed foot in top feeding devices of another basic design are known, e.g., from U.S. Pat. No. 3,935,825, these devices are of a very complicated design compared with the invention and they also require the basic design of the top feeding device to be different.
Accordingly, an object of the invention is to provide an improved transmission mechanism for insuring that the top feed foot of the feeding device is moved with a decreasing velocity as it approaches the touch-down on the material.
A further object of the invention is to provide a sewing machine which is simple in design, rugged in construction and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.